This invention relates generally to the detection of discontinuities, such as holes for example, in tubular members, and more particularly concerns apparatus adapted to be traveled in a well bore and operable to scan the bore and detect the existence of holes in well casing, pipe or tubing.
It is frequently necessary or desirable to obtain information as to the location or depth of holes, cracks or leaks in well casing. For example, such holes may have been produced, as by firing bullets through the casing, to enhance production of well fluid. Accordingly, it may be desirable later to perforate the casing at a selected vertical spacing from the previously formed holes, and the location of the latter must be determined in order to accurately locate that selected spacing. There are other reasons for the need to locate previously formed holes, perforations or cracks in well pipe.
One device usable to inspect tubular members is disclosed in U.S. Pat. No. 4,212,207 to Conradi. That device employs a rotating reflector to reflect ultrasonic waves transmitted toward and received from a bore of a tubular member. One difficulty with using that device in a well bore containing well fluid such as petroleum is the apparent production of cavitation due to rotation of the reflector, and leading to formation of vapor bubbles in the path of ultrasonic wave transmission, and consequent poor signal detection, or signal to noise readings. In addition, the hydrodynamic drag on the rotating reflector requires undesirably high power input to the motor.